The present invention relates to a method of recovering krypton and/or xenon nuclides from waste gases. More particularly, the invention relates to improvements in a method of recovering krypton and/or xenon nuclides which includes adsorption of nuclides in activated carbon or another suitable adsorbent and their desorption from the adsorbent.
Waste gases produced in nuclear power plants and other fuel plants contain krypton and/or xenon nuclides which, as a rule, are radioactive and therefore should not be permitted to escape into the atmosphere. Krypton-85 is particularly dangerous since its radioactivity declines very slowly (half-life period about 10.7 years). Therefore, the contaminated waste gas (normally air) is relieved of solid vaporized fission products, water vapor, hydrogen and oxygen in a first step, and is thereupon caused to contact activated carbon or another suitable adsorbent at extremely low temperatures, preferably in the range of between -70.degree. and -196.degree. C. The activated carbon is thereupon subjected to a desorption treatment at elevated temperatures which yields a product gas containing higher concentrations of noble gases. The enrichment factor in an adsorber which contains activated carbon at a temperature of -40.degree. C is about five. The enrichment factor is the ratio of noble gas concentration in product gas to noble gas concentration in untreated waste gas. Higher concentrations of noble gas can be achieved by arranging several enriching stages in series. The just described conventional adsorption method is quite expensive, mainly because the adsorbing vessel or vessels must be maintained at an extremely low temperature. On the other hand, the concentration of noble gases in the product gas is very unsatisfactory if the adsorption takes place without cooling of the bed of adsorbent in the vessel.